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smoothing off, the trowel should be drawn over the mold, exerting a mod-
erate pressure on the excess material. Mold turned over and operation
repeated.



TESTS. 945

Tests. Am Soc Civ Engrs. Continued.

Weigh the briquettes "just prior to immersiort, or upon removal from the
moist closet," and reject those varying > 3 % from the av.

13. Moist Closet. "A moist closet consists of a soapstone or slate box,
or a metal-lined wooden box the metal lining being covered with felt and
this felt kept wet. The bottom of the box is so constructed as to hold water,
and the sides are provided with cleats for holding glass shelves on which to
place the briquettes. Care should be taken to keep the air in the closet
uniformly moist."

"Where a moist closet is not available, a cloth may be used and kept
uniformly wet by immersing the ends in water. The cloth should be kept
from direct contact with the test pieces by means of a wire screen or some
similar arrangement."

14. Immersion. "After 24 hours in moist air the test pieces for longer
periods of time should be immersed in water maintained as near 21 C
(70 F) as practicable; they may be stored in tanks or pans, which should be
of non-corrodible material."

15. Tensile strength. Solid metal clip, Fig. 5, recommended. No
cushioning between clip and briquette. Briquettes broken immediately
after removal from water. Center the briquette carefully in the clip, to
avoid transverse stresses. Load applied at rate of 600 Ibs per min. "The
average of the briquettes, of each sample tested, should be taken as the test"
of that sample, "excluding any results which are manifestly faulty."

16. Soundness (Constancy of Volume). "In the present state
of our knowledge it cannot be said that cement should necessarily be con-
demned simply for failure to pass the accelerated tests (below); nor can a
cem be considered entirely satisfactory, simply because it has passed these
tests."

Pats of cem paste of normal consistcy (1f 7), abt 7.5 cm (2.95 ins) diam,
1.25 cm (0.49 in) thick at center, tapering to thin edge, made on a clean glass
plate about 10 cm (3.94 ins) square, 24 hours in moist air before test.

(1) Normal test. One pat immersed in water maintained as near 21 C
(70 F) as possible; one in air at ordinary temp. Both observed at intervals
for 28 days.

(2) Accelerated test. A pat is exposed in any convenient way in an
atmosphere of steam, above boiling water, in a loosely closed vessel, for 5
hours.

Pats must remain firm and hard, and show no signs of cracking, distortion
or disintegration. Warping may be conveniently detected by applying a
straight edge to the surf which was in contact with the plate.



946



CEMENT MORTAR.



Sand.*

Composition.

1. The sand,* used in mortar, is ordinarily made up chiefly of grains of
quartz (silica), with some impurities, mostly grains of silicious minerals.
In testing cements, in the laboratory, crushed quartz or some standard
natural sand is used. (See Spec'ns A S C E, under Cement, p. 942.)

2. The silica of the quartz, in sand, undergoes no chemical change
in the mortar; but the use of sand, by diminishing the quantity of cem reqd,
reduces also the cost of the finished work. See remarks on strength, under
Mortar, p 947 i.



OF GRAINS.

3. Screening 1 . Sand and gravel are screened, usually in an inclined
fixed screen, upon which the material is placed by a conveyor, or shoveled
by hand; or in an inclined revolving cylindrical or hexagonal screen, into
which the material is fed.

4. Method of quartering. "To obtain an average sample from
a pile of sand, gravel or stone, the method of quartering is useful. Shovel-
fuls of the material are taken from various parts of the pile, mixed together
and spread in a circle. The circle is quartered, as one would quarter a pie,
one of the quarters is shoveled away from the rest, thoroughly mixed,
spread, and quartered as before. The operation is repeated until the quan-
tity is reduced to that required for the sample." (T & T, p. 281.)

Mechanical Analysis.

5. The mechanical or granulometric analysis of sands,

etc., is the determination, in any given sand or broken stone, of the propor-
tions of grains of diff sizes. It is usually performed by means of sieves or
screens. See If 3. Sometimes, for broken stone, &c., by hand-picking.

6. Fig. 1 shows mechanical analyses of a gravel and a sand by Mr. Allen
Hazen (Mass. State Board of Health, Report 1892, pp. 546-7). In order
to represent both analyses on a single diagram, we have used diff scales for
diams for the two materials.

7. In Fig. 1, the diagrams show, for the two materials there represented,
that

of the sand, 10 % was in grains under, and 90 % over, 0.055 mm diam
" " gravel, 10 % " " " " " 90 % " 34.5 " "



3.0 *



0.5



JU3 EO 30 40 50 60 70



90 100



Fig 1. Sand Analyses.



*By "sand" or

ticles with air, or water, or both; i. e., an aggregation of mineral particles,
with nfoids betw them said voids being filled with



gravel ** we mean a mixture of mineral par-
" mineral particles,
air, or with water, or



with air and water, as the case may be.

Hence, the "volume" of a given quantity of sand or of gravel is the space
occupied by both the solid particles and the air or water or both, filling the
voids.

"Dry sand," or "dry gravel," means: not solid mineral, but a mixture of
dry particles 9f sand (or gravel) and dry air.

The solid mineral portion of such sand or gravel, we designate as "solid."



SAND.



947



Effective Size.

8. The effective size ("e. s.") of a sand or gravel, as defined by Mr.
Hazen (Mass State Board of Health, Report 1892, p 341; Hazen, Filtration,
pp 21, 240) is that size, than which 10 %, by wt, of the grains are smaller, and
90 % larger. Or, the length of the ordinate, at 10 % passing, gives the
effective size. Thus, in the cases just mentioned, Fig 1, we have:



for the sand, e. s. = 0.055 mm; for the gravel, e. s.
Uniformity Coefficient.



34.5 mm.



9. Uniformity coefficient. Similarly, let m = that diam of grain,
than which 60 %, by wt, is smaller, while 40 % is larger. In Fig 1, we have

for the sand, m = 0.46 millimeters;

" gravel, m = 51.00

The uniformity coefficient (" u. c. "), is m/e. s.; and we have:
for the sand, u. c. = 0.46/ 0.055 = 8.4;

" gravel, u. c. = 51.00/34.5 = 1.48.

10. With m = e. s., the unif coeff, u. c., would have its least possible
value, = 1. In general the less nearly uniform a sand is, as to size, the
higher is its "uniformity coeff."

11. In ordinary bank sand, the effective size, e. s., does not vary widely.
Hence the uniformity coefficient, u. c. = m/e. s., varies roughly with that
diam, m, than which 60 % of the grains are smaller, and thus serves as an
indication of the coarseness, as well as of the departure from
uniformity, of the sand. (T & T, p. 182.)

Feret's Method.

12. Mr. R. Feret (Annales des Fonts et Chaussees, 1892, second semes-
tre,) made elaborate experiments as to the effects of fineness of sand, and
the mixture of different finenesses, upon the density, etc., of sand and upon
different qualities of the mortar. He divided his sands into three
finenesses, as follows:

Coarse, c, passing 5.0 mm diam = 4 meshes / sq cm = 5 meshes / lin in
Medium, m, " 2.0 " " = 36 " / " " =15 " / "
Fine, /, " 0.5 " = 324 " / " " = 46 " / "

"Coarse" grains are retained on 2.0 mm diameter; "medium" on 0.5 mm.




Fig 3.

Sand Analyses, Feret.
I



13. The results, obtained in a certain case, with diff mixtures 9f these
three grades of fineness, are shown in Fig 2, which is similar to diagrams
used in connection with alloys of three metals.



947 a



CEMENT MORTAR.



14. After a given mixture has been analyzed, and its percentages of the
three grades thus determined, it is plotted, in the triangle, by a point so
placed that its perp dists, from the three sides, respectively, of the equi-
lateral triangle, are as follows:

distance from side c = percentage of coarse grains;
" m = " medium

" / = " fine

15. The plotting of the points, and the measurements of their dists, are
facilitated by the lines drawn parallel to the three sides respectively.

16. Thus, point a represents a sand having 20 % fine grains, 30 % medium
and 50 % coarse, as shown by the three scales; 20, 30 and 50 being the dists
of a from sides /, m and c, respectively.

17. When a series of experiments has been made, upon any given quality
(as density or porosity, etc, etc) of sand or mortar, as affected by diffs in
mixtures of the three finenesses, they are plotted in this way, and "contour"
or " iso "-lilies are drawn thru those points which represent equal results
in the quality experimented upon. Each "iso "-line therefore represents a
series of diff mixtures, each of which will give the value (as to density or
porosity, etc, etc) represented by it.

18. Thus, in Fig 3 (T & T, p 144, Fig 51) the four contours and the point
(0.610) represent five diff mixtures of coarse, fine and medium sands, said
mixtures having densities (see 1J 20) of 0.525, 0.550, 0.575, 0.600, 0.610,
respectively.

Density.

19. Specific gravity or unit weight. Solid quartz weighs about
165 Ibs per cu ft = 2.643 grams per cu cm; sp gr = 2.64 to 2.67.

20. In mechanics (see p. 338, Art. 14 a) density is defined as the

mass in unit volume. In sand,* the solid portions have practically constant
sp gr. Hence, for a given sand, "density" is used to designate the vol of
solid in unit vol of sand, or the ratio of solid to total vol. This ratio is
sometimes called the "absolute volume." Thus, in unit vol of sand,
"density" = 1 - vol of voids.

21. The greater the density of sand,* the less cement will be reqd for a
given quantity of mortar.

22. The weight, per cubic foot, of a sand,* of given sp gr.
varies directly with its density; and this, in turn, depends upon the shape
of the grains, upon their range of size, upon the compacting accomplished,
as by shaking, tamping, etc, and upon the dryness of the sand.



nt age of total vdfume.

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Weight per unit of volume.
Fig 4. Ratio of Solids and Voids.



* See foot note*, p 946.



SAND. 947 b

23. Fig 4 shows the relation betw (1) the nnit weight and (2) the
percentages of solid and of voids, solid quartz weighing as in t 19.

Effect of Moisture.

24. The effect of moisture, upon the vol of a given quantity of
sand,* is affected by the vol of air introduced, by the quantity of water, and
by the shape of the grains.

See 11 29 to 31.

25. It is impracticable to measure the vol of air introduced, and its
presence vitiates all observations. When sand grains are dropped, one at a
time, into water, most of the air, surrounding the grains, is left behind in
the atmosphere; but when sand* is thrown into water in masses, or when
moist or wet sand is turned over by shoveling, considerable and unknown
quantities of air are entrained with it.

26. In moist sand,* the total (or "absolute") vol of voids is usually
filled partly by water and partly by air.

27. Within a certain limit, moisture increases the adhesion betw the
grains of sand, and thus opposes their sliding, one upon the other, conse-
quently opposing the compacting of the sand; but, beyond that limit, it
acts as a lubricant and facilitates the compacting. See 11 24, 25.

28. Let

V = volume, in cu ft, of dry quartz in 1 cu ft of sand;*

v = " " " " "voids !. .. . y + v = i cu f t;

W = wt, in Ibs, of 1 cu ft of pure solid quartz = 165;

w = " " " " 1 " " " the sand (dry or moist, as the case may be);

d = " " ' " dry quartz in 1 cu ft of the sand; (in dry sand, d = to).

P = " " " water added to 1 Ib of dry sand;*

in (1 + P) Ibs of moist sand;

p = " " " " " " 1 Ib " " " ;

m = " " " " " " 1 cu ft " " " .

Then p/P = 1/(1 + P); and p = P/(l + P);
m = w p; d = w w p = w (1 p)',
V = (w w p)JW = d/165; v = 1 F = 1 d/165;



29. The proportion, p, of moisture (Ibs of water in 1 Ib of moist
sand), is ascertained by heating a known wt of the moist sand, at not less
than 100 C (212 F), until no further loss of wt takes place, and noting the
loss of wt. Then:

p = loss of weight -f- original weight of portion heated.

In dry sand (Fig 4) p = 0, w p = 0, w = d ; and we have:
V = W /W = ii>/165 = rf/165.



Effects of Shape and

SO. Spherical grains. If a number of spheres, of uniform diam,

D, be piaed as closely as possible, the ratio of vol of solid to total vol is



= about 0.74; and the voids (about 0.26 X the total vol) are of t



sizes, such that they can be fitted, respectively, with spheres having diams
= about 0.41 D and 0.22 D. (T & T, pp 169-170.)

31. Effect of gradation of sixes. The proportion of voids may
be indefinitely reduced by adding to, and mixing with, the original grains,
smaller and smaller, or larger and larger, particles, in proper proportions,
each size occupying a portion of the voids left between the particles of the
size next coarser. With spherical particles, therefore, the voids are greatest,
and the wt per unit vol least, when the grains are of uniform size. This
seems to hold true also for particles of other shapes.

* See foot-note*, p 946.
04



947 C CEMENT MORTAR.

Other Properties.

32. Turbidity test for silt in sand. Separate the silt from a
considerable quantity of sand, and make up a special sample containing the
max proportion of silt allowed by the spec'n. Place a small known portion
of this mixture in a known quantity of clear water in a graduated vessel.
Shake the vessel until the sample is thoroly washed. Insert a pin horizon-
tally in the side of a stick near its end, insert that end of the stick into the
vessel, lowering it until the pin is no longer visible thru the liquid, and note
the depth of the pin by means of the graduation. Make several such testa
and note the average depth of disappearance of pin. In testing samples,
if the pin disappears at a higher elevation than the standard, the sand has
more silt than the maximum allowable, and vice versa. (W. J. Douglas,
EN, '06/Dec/20, p 648.)

33. The presence of clay and loam, in sand, may be de-
tected by rubbing the damp sand in the hand, and observing the condition
of the hand, or by mixing the sand with clean water and noting the effect
upon the water.

34. Washing. Dirty sand may be washed in a specially constructed
sand washer; or, by means of a jet from a hose, in a box so arranged that
the mud, clay and organic Jmpurities are floated off, leaving the heavier
sand behind.

35. Washing may carry off the finer particles of a well assorted sand,
leaving it less dense than before. It is well to test a small quantity of the
sand, washed and unwashed, before arranging to wash for use. (Jas. C.
Rain, E R, '05 /Jan/28, p 105.)

36. The degree of sharpness of a sand may be estimated by
means of the sound emitted by it when kneaded betw the hands or more
closely estimated by means of a magnifying glass.



MORTAR. 947 d

MORTAR.*

Constituents.

1. Cement mortar consists of cem, mixt with water, with or without
some inert granular material, as sand, fine gravel, stone or gravel screenings,
or ground cinder. Without sand, etc., the mixture is called neat mortar,
or cement paste.

Amount of Mortar Required for a Cubic Yard of Masonry, f

Mortar.
Description of Masonry. Cu yd.

Min. Max.

Ashlar, 18" courses and H" joints 0.03 0.04

" 12" " " " " 0.06 0.08

Brickwork (bricks of standard size, 8 MX 4 X 2M ins.):

y s " joints 0.10 0.15

y s " to M" joints 0.25 0.35

%" to H" joints 0.35 0.40

Rubble, of small, rough stones 0.33 0.40

" large stones, rough hammer-dressed 0.20 0.30

Squared-stone masonry, 18" courses and M" joints 0.12 0.15

" 12" " " 0.20 0.25

2. Effect of roasting and of subsequent wetting. The
materials, of which cem is made, are inert or stable compounds, remaining
practically unchanged under ordinary conditions; but when, in burning,
the calcareous materials are subjected to high temps, either alone or mixed
with argillaceous materials, relatively unstable compounds are formed,
ready to enter into new and again stable compounds when their particles
are brought into intimate contact by being mixed with water, the water also
entering into the new combinations. The mixture then soon "sets" (loses
plasticity), and, shortly thereafter, begins to solidify and harden.

See f 8, Cement, p 931.

3. In the process of crystallization, the alumina appears to act chiefly as
a flux, promoting the formation of the lime silicate, upon which the success
of the operation depends. Iron oxide, which is generally present, seems to
answer as well as alumina, as a flux, and it, requires a less high temp for
calcination.

4. The proportion of sand, which should be used in any given case,
cannot be properly stated without stating also its range of .size, or the
proportion of voids to the whole mass; but, in general, good Portland cems
will "carry" from 2 to 3 vols of sand; nat cems from 1.5 to 2 vola.

5. Approximate quantities of Portland cement and loose
sand per cu yd of mortar.

Neat 1:1 1:2 1:3 1:4 1:5 1:6

bbls cem 8.0 4.6 3.1 2.3 1.8 1.5 1.3

cu yds loose sand 0.65 0.87 0.97 1.02 1.06 1.10

Cement in Mortar.

See also CEMENT, p 930.

6. Owing to the cheapness with which cements are now manufactured,
and the superiority of the mortars made from them, the latter have to a
great extent superseded lime mortars, even in ordinary building
operations.

7. In selecting cem, a reputation, gained by years of successful use
and experiment, is of greater value than the results of a few tests; but such
tests are of value for excluding inferior parcels of such accepted brands.

8. High grade cements are usually economical, even at a
higher cost, as they allow the use of a larger proportion of the cheaper in-
gredients, sand, gravel and 'broken stone.

*As the strgth, permeability, etc, of a cone depend largely upon those of
its mortar, we discuss, under "mortar," many of its properties commonly
discussed under "concrete"

t Taken, by permission, from "A Treatise on Masonry Construction " by
Prof. Ira O. Baker. New York, John Wiley & Sons. 9th edition 1907



947 e CEMENT MORTAR.

9. Free Lime. Gem may contain "free" (uncombined) lime as a
result (1) of insufficient manipulation of the raw materials, (2) of insufficient
burning, (3) of an excess of lime carbonate (CaCO 3 ) in the raw materials, or
(4) of adulteration after burning and grinding.

10. This lime may be present either as quick lime, CaO, or as slacked
lime Ca(OH) 2 , either of which may be washed out (the CaO first becoming
Ca(OH)^) by infiltrating water. This, of course, weakens the cem.

11. Slacked lime takes no part in the hardening process, but remains
as an inert filling material.

12. Quick lime slacks by absorption of the water used in mixing;
and, when the burning has been at a high temp, the slacking is delayed. If
it takes place during the setting of the cem, the swelling of the lime weakens
the cem by rendering it porous. If slacking is delayed until after harden-
ing, and if the expansive force is sufficient, the cem is disintegrated.

13. Excess of lime retards setting, and reduces soundness.

14. Free Magnesia. Much uncertainty exists as to the effect of free
magnesia, in diff proportions, in cem. Like lime, it expands when wet, but
much more slowly; and its presence may therefore remain unsuspected until
too late. Dolomite, or magnesian limestone, contains about 45 % of
magnesia. Formerly, 1.5 % of free magnesia, in cem, was considered dan-
gerous. It is now generally believed that more than from 3 to 5 % weakens
the cem, and that 8 % or more causes cracking. In any proportion, it is
probably objectionable, at least as displacing an equal quantity of the more
valuable lime.

Sand* in Mortar.

See also SAND, pp 946, &c.

15. The quality of the concrete depends upon the strength of the mortar,
and this, in turn, depends largely upon the character of the sand.

16. For a given proportion by wt, the best sand is that which produces the
smallest vol of plastic mortar.

17. Weight. As betw two sands, of a given material, the heavier of
course has the smaller vol of voids.

18. Fineness. A fine sand, well assorted as to sizes of grain, and
therefore dense, may make better mortar than a coarser sand, with grains
of more nearly uniform size and therefore less dense.

19. Extreme fineness prevents penetration of the paste betw the
grains, and delays setting.

20. Mortars made with fine sand, altho less permeable than those made
with coarse sand, are apt to be more easily acted upon by sea water.

21. Shrinkage. Mortars, with coarse sand, shrink less than those
with fine sand.

22. Sharpness. It has been customary to insist upon sharpness of
grain, in sand used for mortar, probably owing to the impression that sharp
grains form a better bond with the cem or that sharpness indicates freedom
from impurities; but the advantage is doubtful. Sands with rounded
grains are commonly used, and with entirely satisfactory results; and the
laboratory tests generally indicate that sharp-grained sands have no marked
superiority Roundness of grain facilitates the packing, and thus increases
the density of the sand.

23. The Board of Public Works of Porto Rico, with briquettes of 1 : 2
mortar, found 25 % greater strgth with washed than with unwashed
sand. Sand, containing much foreign matter, should be tested before being
accepted.

24. In general, the evidence, as to the relative values of sand
and of screenings, appears to be favorable to the use of screenings (see
Experiments), but opinion is divided. The hydraulicity of the dust,
in the screenings, may add to the strength of the mortar.

25. Harry Taylor, Capt, Corps of Engrs, USA, tested 1650 briquettes
of 1 : 3, 1:4 and 1 : 5 mortars, at 1, 3, 6 and 12 mos, with standard crushed
quartz, Plum Island sand and crusher dust. Crusher dust gave briquets

* See foot-note, SAND, H 1, p 946-



MORTAR. 947/



2.3 times stronger than sand, and 72 % stronger than quartz. 1 : 5, with
stone dust, stronger than 1 : 3 quartz.

26. G. J. Griesenauer, E N, '03 /Apr/16, p 342. Chicago, Mil & St P RR,
225 tests, as follows :

Limestone screenings, 1 : 3, passing No 12, held on No 40 sieve,
averaged 74 % better than Hammond pit sand, 1:3; with all sizes used,
they averaged 115 % better. Mortar of 1 : 6 screenings was 23 % stronger
than 1 : 3 sand. Gravel screenings were not much better than sand.

27. Maryland highways. Briquettes, made with stone screenings,
^ere 34 to 62 % stronger than with Potomac River sand.

Liime in Mortar.

28. The substitution of 10 % to 20 % lime paste for an equal
vol of cem paste, reduces the cost of the mortar, renders it less "short",
and slightly retards setting, without seriously diminishing its strgth. Larger
quantities reduce strgth. (Baker, Masonry Construction.)

29. Feret found the effect of lime dependent upon the richness of the cem
mortar. With 1 : 4 cem mortar, the addition of 4 to 5 % of dry slaked lime
increased the strgth; while, with 1 : 1.25 cem mortar, the addition of lime
lowered the strgth. (Chimie Appliquee, 1897, p 481.)

Clay in Mortar.

30. Laboratory tests indicate that a small admixture of clay

increases rather than diminishes the strgths of mortar, and diminishes its
permeability; but, in actual work, the clay particles tend to adhere and
thus to form lumps having but slight cohesion.

31. Laboratory conditions, as to dryness, pulverization, etc., cannot be
reproduced in practice.

32. When the clay occurs naturally in the sand, it may not be practicable
to effect a perfect mixture and distribution.

33. Clay, etc, are more likely to give trouble with dry than with wet
mixtures.

Consistency.

34. Relative strengths of dry and wet mortars, 1:1. Alfred
Noble, over 5000 experiments. Strength of dry mortar taken as 100.

Portland cement Natural cement



Age 30 days 3 mos 6 mos 1 yr 30 days 3 mos 6 mos 1 yr

Dry Mortar 100 100 100 100 100 100 100 100

Moderately stiff. 97 94 97 97 78 89 95 90

Grout 90 92 91 95 63 77 86 82


1 2 3 5 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

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